Antenna-based communication systems may utilize beamforming in order to create steered antenna beams with an antenna array. Beamforming systems may adjust the delay and/or gain of each of the signals transmitted by (or received with in the receive direction) the elements of an antenna array in order to create patterns of constructive and destructive inference at certain angular directions. Through precise selection of the delays and gains of each antenna element, a beamforming architecture may control the resulting interference pattern in order to realize a steerable “main lobe” that provides high beamgain in a particular direction. Many beamforming systems may allow for adaptive control of the beam pattern through dynamic adjustment of the delay and gain parameters for each antenna element, and accordingly may allow a beamformer to constantly adjust the steering direction of the beam such as in order to track movement of a transmitter or receiver of interest.
Beamforming architectures may conventionally employ one or both of digital and radio frequency (RF) processing in order to apply the desired delay and gain factors at each element of the array. Phased antenna arrays are a particularly favored RF beamforming technique for narrowband signals which relies on the approximate equivalence between phase shifts and time delays for narrowband signals. Accordingly, phased antenna arrays may place an RF phase shifter in the signal path of each antenna element and allow the individual phase shift values to be adjusted in order to steer the resulting antenna beam. Although many phased array designs achieve sufficient performance with phase-only control, variable gain amplifiers and other techniques such as tapering may additionally be implemented in order to also allow for gain adjustment.
In contrast to the analog RF processing of RF beamformers, digital beamformers may employ digital processing in the baseband domain in order to impart the desired phase/delay and gain factors on the antenna array. Accordingly, in digital beamforming systems, the phase and gain for each antenna element may be applied digitally to each respective antenna signal in the baseband domain as a complex weight. The resulting weighted signals may then each be applied to a separate radio frequency (RF) chain, which may each mix the received weighted signals to radio frequencies and provide the modulated signals to a respective antenna element of the antenna array. As each antenna element in a digital beamforming system requires an exclusive RF chain, many digital beamforming solutions may require a substantial amount of hardware and thus have considerable cost and power-consumption rates.
Hybrid beamforming solutions may apply beamforming in both the baseband and RF domains, and may utilize a reduced number of RF chains connected to a number of low-complexity analog RF phase shifters. Each analog RF phase shifter may feed into a respective antenna element of the array, thus creating groups of antenna elements that each correspond to a unique RF phase shifter and collectively correspond to a common RF chain. Such hybrid systems may thus reduce the number of required RF chains by accepting slight performance degradations resulting from the reliance on RF phase shifters instead of digital complex weighting elements.